The admixture of charcoal with the soil, is said to be a means of adding to its nutritive qualities. Charcoal, which is nearly pure carbon, may be supposed continually to give off a portion of this gaseous substance during its decomposition, and this uniting with a portion of the oxygen contained in the air, would furnish a supply of carbonic acid gas, to the atmosphere immediately about the plants. It should however be borne in mind, that charcoal, is a substance whose decomposition except under the influence of heat, proceeds very slowly indeed, and therefore its chemical influence must not be overrated: doubtless however, the small portion which does combine with the oxygen of the air, is directly beneficial to the plants; for it is a function of the vegetable kingdom by the action of their leaves, when under the influence of light, to decompose carbonic acid, the oxygen of which is liberated, and the carbon fixed in the living tissue. It is therefore probable that a supply of carbonic acid, artificially maintained about the leaves and stems of plants, may be beneficial to them, by furnishing them directly with a portion of carbon, which they cannot absorb in a seperate state. When the charcoal is made from twigs, and the small branches of trees, its decomposition is often more rapid, than when it is obtained by the usual course of manufactering it: if the latter kind of charcoal is employed, it should be broken into pieces of a small size; and in ordinary cases, it should not be used in larger proportion than with about twice its bulk of soil, with which it should be intimately blended. Besides its chemical action, which is probably beneficial, charcoal has a decidedly advantageous mechanical action in the composition of soils, and this is of a twofold nature:--first, in common with any similar materials, it renders the soil "open," and thus effectually favours the free passage of water through its mass: secondly, it serves as a perpetual reservoir of moisture in the soil, for in consequence of its being extremely porous, it imbibes a great quantity of water, by its force of attraction, and this it parts with slowly to the soil; in this way, there is no doubt that its action is most salutary. Probably a few pieces of charcoal placed perpendicularly in the soil, and kept continually _wet_, by the action of some little capillary contrivance, would serve as the best possible means of conducting moisture, and distributing it to the roots of plants.